Rock bolts for supporting structures e.g. roofs of passageways in mines are well known. There are many different types of rock bolts. A rock bolt generally consists of an elongate shank (length will generally depend upon the material which the rock bolt is intended to secure) having a distal end (the end which in use is fixed furthest within the rock), or “head end”, and a proximal end (the end, in use, which is closest to the surface of a rock and, in many cases, may actually project from the rock surface), or “tail end”.
Rock bolts are fixed in elongate boreholes (not much wider or even slightly less in width than the rock bolt) which is drilled in the rock. In use, a bearing plate is secured at the tail end of a rock bolt fast against the rock surface. The rock bolt and bearing plate assembly operate to support the rock. Many rock bolts may be used to support structures. For example, in mines rock bolts may be used to support passageways.
Installation usually requires drilling of the borehole by using a drill rig and a drill steel (a long steel rod with a drill bit on the end). The drill steel is then removed from the borehole. Resin (or “grout”) is inserted into the borehole, then the rock bolt itself is inserted and tightened up against the bearing plate.
Some rock bolts incorporate point anchoring mechanisms, which can be manipulated post insertion of the rock bolt to mechanically interfere with walls of the borehole in order to firmly secure the rock bolt.
The conventional procedure for installing rock bolts can be relatively time consuming in the context of efficient mine operation. It requires a number of separate tasks (affixing the drill steel, drilling the borehole, removing the drill steel, inserting the resin and rock bolt, securing the rock bolt) which require time and a significant amount of labor. In a mining situation, where it is important that mining shafts, passageways, etc be created quickly (as this directly affects the economic operation of the mine), this is a disadvantage. Further, the drill steel and drill bit are consumables which add to the cost of installing rock bolts.
“Self drilling” rock bolts are known. These generally incorporate a drill bit as part of or connected to the head end of the rock bolt, the tail end being attachable to a drill rig in order to drill the borehole. Once the hole is drilled, the rock bolt is retained in the hole. Whilst self drilling rock bolts have the advantage of speed of application, grouting can be difficult and there are no provisions for any point anchoring mechanism to firmly secure the rock bolt.